When an engine is operated in an idle mode, oil pressure in an oil circuit supplying oil to various engine components, may decrease substantially. Consequently, the oil pressure in the oil circuit may also decrease substantially, and the oil circuit may not reliably supply oil or provide adequate oil pressure to various engine components such as a hydraulic actuating device of a switchable valve drive. When the engine is switched off, the oil pressure in the oil circuit may fall abruptly, and the oil in the circuit may drain via gravity through a return oil line to oil pan.
The engine may be switched off for various reasons, such as when parking the vehicle, for example. However, switching off the engine may also take place during a start-stop strategy, in which the engine is switched off when there is no current power requirement, rather than continuing to operate the engine at idle. In practice, this means that the engine is deactivated, i.e. unpowered, at least when the vehicle is at a standstill.
If the engine is started or restarted, there is need to increase the oil pressure in the oil circuit. In addition, some of the lines in the oil circuit, which have emptied owing to the engine being switched off, must be refilled with oil before the oil pressure in these lines may be increased. These processes take time, typically a few seconds, especially lines in the oil circuit which are geodetically at higher points may be severely affected, such as oil lines in the cylinder head, e.g. a rising line leading into the cylinder head and a main oil line extending in the cylinder head. Consequently, the engine components receiving engine oil from these lines may not receive engine oil or adequate oil pressure in a timely manner, especially during engine start.
Attempts to address delayed supply of engine oil to various engine components include use of check valves in the oil circuit. One example approach is shown by Lee in US 2008/0135003. Therein, an oil supply circuit in an engine comprising a first and a second oil circuit for supplying engine oil to a plurality of tappets of cylinders via a hydraulic pump is disclosed. Each of the first and second oil circuit is configured with a control valve to control flow of oil in each circuit. The use of check valves in the oil circuits is designed to counteract emptying of oil lines.
However, the inventors herein have recognized potential issues with such a system. As an example, the use of check valves in the oil circuit may entail a pressure loss in the circuit, which may reduce oil pressure transmitted to engine components during engine operation. Further, check valves in the oil circuit may malfunction due to various causes, and may affect transmission of oil to various engine components.
The inventors herein have developed an oil circuit design to at least partly address the above issues. In one example design, an oil circuit may be provided comprising: a rising oil line from a block to a cylinder head of an engine; a main oil line in the head; and an oil siphon system including a reservoir positioned between, and having at least one portion at a lower elevation than both, a section of the rising line and a section of the main oil line so that oil flows into, and remains in the reservoir when the engine is shut-off. In an additional example, the rising oil line, the main oil line and the oil siphon system are a sealed system, and oil remains in the reservoir and at least a portion of the main line and a portion of the rising line after the engine is shut-off. In a further example, engine components receive oil upon engine start without an interruption in oil delivery. In another example, the oil siphon system and reservoir form essentially a u-shape connected between the rising and main oil lines, and engine components receive oil upon engine start without an interruption in oil delivery. The components include one or more of the following; a valve train, a variable valve drive, a camshaft, or a camshaft adjuster.
In this way, the design of the oil circuit may be used to improve oil supply to engine components while minimizing delays during engine startup. For example, the siphon system may reduce an abrupt drop of oil levels within the oil circuit when the engine is switched off. In this way, the oil circuit design may confer several advantages. By reducing the drop of oil levels in the oil circuit, the siphon system may provide a method of supplying engine oil to engine components during engine startup to minimize delays in engine response. Further, the oil circuit is a valve-less system that minimizes large pressure drops within the system to improve engine performance.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.